OLD School (compliments of Stack Overflow forum) for less fortunate users who do not allow to have a CLR-enabled SQL Server:

http://stackoverflow.com/questions/15523789/sql-email-verification-function-using-regex

Solution is based on legacy COM VBScript library, but still works.

My $0.02 - I personally would use Regex expression for data quality check, in production just to validate a scalar values. 😎